Process of converting coal to liquid products



PROCESS OF CONVERTING COAL TO LIQUID PRODUCTS- Filed July 15, 1969 2 fil S 5 a u INVENTOR:. m a MlLTON M. WALD ms ATTORNEY United States Patent Ofice 3,542,665 PROCESS OF CONVERTING COAL T LIQUID PRODUCTS Milton M. Wald, Walnut Creek, Calif., assigmor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed July 15, 1969, Ser. No. 841,843 Int. Cl. Cg 1/06 US. Cl. 208-10 8 Claims ABSTRACT OF THE DISCLOSURE Coal is converted to liquid hydrocarbon products by passing it through a continuous phase catalyst system selected from antimony trichloride, tribromide or triiodide; bismuth trichloride or tribromide; or ansenic triiodide; maintained at a temperature between 200 and 550 C. and under hydrogen partial pressure of at least 250 p.s.i. whereby the catalyst system performs the functions of acting as a hydrogenation catalyst, acting as a cracking catalyst, and providing a medium for maintaining the reactants in suitable relation to one another to promote reactions and obtain benefiical product distribution.

BACKGROUND OF THE INVENTION For a long time coal has been of interest as a starting material for production of liquid fuels because it is composed of compounds of carbon and hydrogen, with some sulfur, oxygen and nitrogen. Although technology for coal liquefaction has been available for some time, there is no commercially economic process available. The incentive for developing a commercially economic process for converting coal to liquid hydrocarbon products is particularly increased as discovery of new crude oil sources becomes more difficult. In the continental United States, known reserves of coal are sufficient, if converted, to provide liquid fuel for the United States for several hundred years.

For many years, coal has successfully been converted to liquid hydrocarbon products. Although these conversions may be accomplished successfully in the laboratory, they cannot be accomplished successfully on a commercial scale for a number of reasons. One. reason is that it is necessary to hydrogenate coal in converting it to such liquid products in order to avoid production of large amounts of less valuable products such as char and sludge, and to produce the desired liquid hydrocarbon product. Extremely high hydrogen pressures have been required for this hydrogenation. The expense and engineering difficulties of operating at hydrogen pressures of 2500-4000 p.s.i. and higher result in such high production costs that the products are not commercially competitive with those from crude oil. Temperatures of 400450 C. have also been required for conversion, and these high temperatures lead to excessive production of such less valuable products as methane. Moreover, the high heteroatom content of the coal, and the presence of polynuclear aromatic structures, cause rapid deactivation of most catalysts. The hydrogen sulfide formed from the sulfur in coal is an effective poison for metallic hydrogenation catalysts, while the water and ammonia formed from oxygen and nitrogen deactivate acidic cracking catalysts.

The composition of coal also includes ash which is solid phase mineral material that cannot be converted to liquid products, and the ash accumulates in beds of solid catalysts diminishing their activity by dilution, by masking the catalyst, and by clogging the catalyst beds to prevent the free flow of material through them. Even with expensive coal preparation processes for removing ash, the

3,542,665 Patented Nov. 24, 1970 length of time that a catalyst bed may be employed is limited by the amount of ash within the feed that cannot be removed. The ordinary conversion of coal to liquid products results in the formation of char which is a solid phase residue and it, too, interferes with catalyst activity by clogging and dilution.

Accordingly, although it is known that hydrogenation and cracking of coal will produce a petroleum-like liquid product, difliculties such as those enumerated above have prevented commercial realization of processes to convert coal to a useful liquid fuel.

THE INVENTION The invention deals with a process for converting coal to liquid hydrocarbon products, which process avoids or greatly mitigates the above-enumerated problems. The process of this invention employs at least one of a particular group of catalysts in a triple role which causes extremely high conversion of coal to useful liquid products at reasonable operating conditions which avoid the problems usually associated with coal conversion.

These catalysts have extremely high catalytic activity and therefore give high conversion of the coal at moderate temperatures and pressures. Under the reaction conditions usable with the catalysts of this invention, it is possible to obtain a much more favorable product selectivity. Much less than the usual amount of propane and lighter hydrocarbons are formed thereby greatly saving on the amount of the costly hydrogen gas required for the coal conversion. Because of the high and selective cracking activity of the catalyst, a much larger part of the liquid product than usual boils within the range normally used for gasoline, and therefore less further processing is required. Moreover, the gasoline-range portion of the liquid product contains a high percentage of desirable isoparaffin hydrocarbons, which are high octane components, and of cycloparaifin hydrocarbons which are excellent feeds for catalytic reforming. The catalysts are insensitive to the amounts of water and hydrogen sulfide formed which often are catalyst poisons and their effectiveness is not diminished by the presence of normal amounts of solids such as ash and char.

The process of the present invention involves the use of a continuous liquid phase catalyst system which is selected from antimony trichloride, tribromide or triiodide; bismuth trichloride or tribromide; or arsenic triiodide as a catalyst to promote hydrogenation, as a catalyst to promote cracking, and as a liquid medium in which the desirable conversion reactions take place readily. The conversion of coal into liquid products is effected in the continuous liquid catalyst phase at temperatures between 200 and 550 C., preferably between 275 and 400 C., Where the reaction is effected at a reasonable rate without producing too many normally gaseous products, and in a temperature range where hydrogenation reactions are more favored.

The reaction is also effected at hydrogen partial pressures of at least 250 p.s.i., preferably at least 800 p.s.i., to provide sufiicient driving force for hydrogenation. While higher partial pressures of hydrogen have no adverse effect on the conversion, extremely high pressures are to be avoided because of the engineering difficulties and high costs involved in attaining and maintaining them. It is a significant advantage of this invention that results near 0ptirnum are obtained at pressures below 2000 p.s.i.,g.

The process of this invention may be operated either in batch or continuous manner and preferably is operated continuously for the usual reasons of high production rates and higher efficiency.

When the process is operated continuously coal may be introduced into the reaction zone either ground finely and suspended as a pumpable slurry, or as a dry solid. If fed dry, coarsely ground coal may be employed in that the coarse coal particles disintegrate in the continuous phase catalyst. The liquid phase employed for slurrying the coal is advantageously recycled catalyst, or a coal extract or other heavy oil fraction that is benefited by the hydroconversion reaction conditions and it also preferably contains recycled material separated from the liquid product of the process.

Hydrogen is preferably introduced beneath the surface of the continuous catalyst phase so that it is absorbed in the catalyst and available to hydrogenate coal prior to or simultaneously with cracking reactions that are affected. The hydrogen may be from any source and need not be pure. For example, hydrogen resulting from a reforming process that contains light hydrocarbon, hydrogen sulfide or water may be employed. The hydrogen preferably is introduced either mingled with the coal feed or at least beneath the surface of the continuous catalyst phase in the form of finely dispersed bubbles, and hydrogen is preferably separated from other vaporous products of the conversion and returned to the reaction vessel. The manner of introducing hydrogen may be used to stir the system, and additional stirring may be provided if required.

It was unexpected that the continuous phase metal halide catalysts of this invention were not poisoned by water and hydrogen sulfide formed by hydrogenating heterocyclic molecules. These materials appear to pass through the catalyst system and appear in the product without significant effect on the catalyst. Water particularly is usually very destructive of Friedel-Crafts type catalysts by forming inactive hyrolysis products. Coal is known to contain large amounts of organically bound oxygen frequently more than 20% by weight in some coals and usually around by weight, and severe catalyst poisoning problems in employing a Friedel- Crafts-type catalyst should be anticipated. However, the metal halide catalysts of this invention, as distinct from many other Friedel-Crafts-type catalysts, are not adversely affected by oxygen compounds or water, and in fact, the effect of water on the catalyst is so slight that close attention to drying the coal before introducing it into the process is not necessary. The catalysts are similarly unaffected by organic sulfur compounds or hydrogen sulfide.

However, the metal halide catalysts are affected by nitrogen compounds or by ammonia which is the hydrogenation product of the nitrogen in heterocyclic molecules. It appears that ammonia-metal-halogen complexes from which are stable compounds and the reactions forming them are not reversible at conditions within the reactor. However, since the nitrogen content of coal is small compared with the oxygen and sulfur content, and since the continuous phase of catalyst is very large compared with the nitrogen content of the coal, the complexes that form do not make the process uneconomical. In a continuous process in accordance with this invention, ammonia-metal-halogen reaction products may either be removed, and make-up catalyst added as required, or the catalyst may be subjected to regeneration. With regard to the latter process, regeneration may be effected on a slip stream of catalyst so that an equilibrium inventory of complex is maintained in the total catalyst body, and desirably a slip-stream of catalyst will be circulated from the main body to a separate regenerating zone where ash and char are removed as well.

As stated above, the metal halide catalysts are surprisingly active and durable as catalysts for hydrotreating of coal to produce liquid products. The reactions promoted are cracking, as evidenced by the low boiling point of the product compared with the solid character of the charge, and hydrogenation, as evidenced by hydrogen take-up during processing and the saturated nature of 4 the product, as well as by the decrease of residual products.

The following examples are presented to illustrate various aspects of the present invention and are provided to be illustrative rather than limiting the scope of the invention.

EXAMPLE 1 The nature of the product obtained by the process of the present invention is illustrated in Example 1. In Example 1, Illinois No. 6 coal ground to between 60-200 mesh was employed as the charge. Although the coal as received had high moisture and ash content, for purposes of determining conversion, the analysis of the coal is reported on a moistureand ash-free basis. The coal contained 10.5% w. organic oxygen, 1.5% w. organic nitrogen, 2.2% w. organic sulfur, and 85.8% w. carbon and hydrogen. Accordingly, if the carbon in the coal were converted stoichiometrically with hydrogen to octane, grams of moistureand ash-free coal would yield only 94 grams of octane. On a moisture-free basis 100 grams of coal would yield only 81 grams of octane. In general, conversion is measured as the amount of material in the product extractable in toluene expressed as the percent of the charge. As indicated above the charge may be considered total, but is more accurately considered on a moistureand ash-free basis.

The experiment described herein was an autoclave experiment and it employed 150 grams of antimony tribromide as the continuous liquid phase catalyst and 30 grams of coal. Hydrogen pressure of about 1,800 p.s.i. was employed, and the reaction was carried out for 30 minutes at a temperature of 350 C. The hydrocarbon product from the process was as follows:

Percent w. Propane and lighter 2.1 Butanes 4.8 Pentanes and hexanes 7.3 Cyclo-C H 6.8 C7+Cg hydrocarbons 14.8 Hydrocarbon boiling above C and below 250 C. 19.5 Liquid boiling above 250 C. 29.5 Char (Insoluble carbonaceous material) 4.2 Water 11.1 Hydrogen sulfide 4.5 Ammonia 1.8

Total 106.4

The hydrogen charged to the process amounted to 6.4% w. of the coal charge and this amount should be subtracted from the total yield to make a weight balance of 100%.

To complete the above analysis, it should be brought out that the liquid product boiling below 250 C. was examined for hetero-atom content and the analysis indicated that parts per million of organic sulfur still remained in the product, 0.09% weight organic oxygen still remained in the product, and that no organic nitrogen could be detected. The foregoing example establishes that of the carbon and hydrogen in the coal charged to the process, all of it was converted to useable hydrocarbon except 4.2% that remained as char. The example also establishes that the liquid product from the process is highly suitable for use as hydrocarbon fuel or for charging to a petroleum conversion process in that it is substantially free of oxygen, sulfur, and nitrogen which are troublesome ingredients in processing of petroleum.

EXAMPLE 2 Since the water produced in hydrotreating coal shows no adverse effects on the catalyst activity, an experiment was conducted to determine whether large amounts of water would produce hydrolysis or other poisoning reactions. Duplicate runs were made in an autoclave employing 150 grams of antimony tribromide, 20 grams of coal, 1800 p.s.i. of hydrogen pressure and temperatures of 350 C. The runs were for 60 minutes each and were conducted under identical conditions as far as could be maintained except that in one run 7.5 grams of water was added to the autoclave. Following the identical runs, the product from each was analyzed. In the water-free run 97% conversion was effected while in the water-containing run 96% conversion was effected. The product distribution in the two runs was substantially the same, in one case 57.3% by weight (basis coal fed) of materials boiling up to 250 C. was produced, and in the other case 57.8% w.

A similar test to determine the effect of hydrogen sulfide was run with hydrogen sulfide added to one reactor. This test produced substantially the same results, thereby demonstrating that the catalyst is resistant to hydrogen sulfide as well as water.

EXAMPLE 3 To establish the effects of ammonia on the reaction, identical autoclave tests were run employing 150 grams of antimony tribromide, 20 grams of ground coal, hydrogen pressure of 1800 p.s.i. and a reaction temperature of 300 C. In one case the autoclave also contained 8.1 grams of ammonia, again in excess of what would be produced by processing ordinary coal. An analysis of the product showed that the ammonia-poisoned catalyst produced a useful liquid product. However, the product was high boiling indicating that it was hydrogenated to a large extent but cracked very little. Only 5.7% of the liquid product from the poisoned catalyst boiled below 250 0.; however, hydrogenation of the coal appeared to be effectively accomplished and a useful product produced, although very small amounts of it boiling in the gasoline boiling range were found.

EXAMPLE 4 Although antimony tribromide is the preferred catalyst of this invention, antimony trichloride, antimony triiodide, bismuth trichloride, bismuth tribromide and arsenic triiodide may be employed when different processing conditions or product distributions are desired. In evaluating the metal halides useful for this invention, a series of tests was run under indicated conditions. In each test 20 grams of coal was employed with enough molten catalys to produce a continuous phase in an autoclave maintained at 1800 p.s.i. hydrogen prssure. All analyses are based on moistureand ash-free coal, or in other words, on conversion of material that it is possible to convert. The products from the various tests are recorded below in Table I.

TABLE I Catalyst .L stool, Sbl; Biol, BiEBr Asr,

Temperature, C 350 350 325 265 325 Products, g./100 MAF coal' C1 C2 1.2 1.7 1.8 0.4 1.3 Cs 2.8 1.6 8.1 1.6 0.6 C4" 7. 7 3. 9 16. 5 6. 0. 8 6.2 3.0 8.9 3.7 0.9 Ca 9. 6 8. 3 9. 1 7. 4 5. 6 Uri-Ca..- 14. 1 12. 4 l1. 5 12. 5 8. 0 O 250 E1 10. 9 25. 2 7. 4 16. 3 l5. 6 H dro en consume Ii/IA coal 5. 5 5. 9 7. 8 5. 4 5.0

The data in Table I indicate that all of the claimed catalysts have good activity for converting coal to liquid products. The total conversions in every case were 90% or higher on an MAF basis. The data in Table I are not intended to be comparative. Rather they indicate only that each material is elfective. Adjustment of temperature in particular and other conditions can produce various products from the same charge employing the same catalyst.

6 EXAMPLE 5 Example 5 is presented to illustrate the effectiveness of the catalyst system and process of this invention even at very low hydrogen pressure. In Example 5 an autoclave was charged with 200 grams of bismuth tribromide and 20 grams of Illinois No. 6 coal. Hydrogen was added to the autoclave to a pressure of 250 p.s.i.g. and the contents of the autoclave were heated to a temperature of 350 C. for 60 minutes. The resulting product reported as grams per grams of MAF coal was as follows:

As stated above, it is desirable to maintain the catalyst body in the reactor at some operable equilibrium level of contamination with regard both to the ammoniametal-halogen complex and with regard to solids such as ash and char. One method for maintaining the equilibrium catalyst activity is to remove a slip-stream from the body of molten catalyst in the reactor and subject it to a separation process for separating metal trihalides from non-catalytic material, to regenerate metal trihalides from the complex, and to discard char, ash and other nonuseful solids. Although any number of regeneration schemes may be employed, one useful scheme is as follows.

A slip-stream of liquid phase from the catalyst bed is removed and subjected to extraction with hot toluene or other available aromatic solvents. Toluene is a highly selective solvent for the metal trihalides used as catalysts, and for liquid hydrocarbons. This extraction produces an extract stream containing toluene, hydrocarbon, and metal trihalide from which the toluene may easily be removed by flashing, and metal trihalide and hydrocarbon may be returned to the reaction vessel, and a raffinate stream that will consist largely of ammonia-metal halogen complex, any metal that was formed by reduction, char and ash. The rafiinate stream may be subjected to high temperature treatment which wll cause the complex to decompose to ammonium halide, and metal trihalide, so that regenerated metal trihalide may be returned to the reaction Zone while solid phase ash and char may be discarded.

The regeneration and cleaning process suggested above is exemplary only and others may be employed with equal success. Of course, the rate at which such regeneration and cleaning is effected will be determined to a large extent by such factors as the nitrogen content of the coal, the ash content of the coal, and the rate at which char is produced in the conversion process. With a continuous phase catalyst, however, the regeneration process can function with a great deal of latitude in that exception ally large quantities of catalyst will be present in active condition even under circumstances where a great deal of catalyst contamination exists.

To better describe the present invention, the accompanying drawing is provided. The drawing illustrates schematically a flow diagram representing one process embodying this invention and, being highly schematic, it does not illustrate heaters, valves, instrumentation and other conventional equipment that would normally be employed in such a process.

In the drawing a vessel 1 is supplied with ground coal via line 2, liquid hydrocarbon recycled from the process as hereinafter described through line 3 and, if desired, a heavy oil, such as a residual fraction from a petroleum refining operation, or a coal extract supplied through line '5. In vessel 1 a slurry is formed between the liquid and solid phases. The slurry contains sufficient liquid to be pumpable and it passes through line 6 into the suction side of pump 7. In pump 7 the pressure of the slurry is raised to reaction pressures, preferably about 1800 p.s.i., and it passes through line 8 into the lower portion of reactor 9.

In reactor 9 a large pool of catalyst preferably antimony tribromide, is maintained in suflicient quantity to be a continuous phase during the reaction process. The slurry, introduced beneath the body of liquid antimony tribromide passes upwardly through it, preferably distributed as fine droplets and particles. Hydrogen gas is also introduced beneath the catalyst liquid level through line 10, the hydrogen gas being partly recycle gas recovered from the product and partly fresh hydrogen gas introduced into the system through line 11.

Within reactor 9, which is maintained at 350 C. preferably by adjusting the temperature of the slurry before it enters the reactor, the cracking and hydrogenation reactions occur within the liquid catalyst medium and a product of normally liquid hydrocarbons, which are in vapor phase at reaction conditions, discharge from reactor 9 through line 12. The material in line 12 is cooled and flashed in phase separator 13 to remove a recycle hydrogen stream and the resultant liquid product from the process passes through line 15 into fractionation column 16. In fractionation column 16, light products are passed overhead through line 17 while the heavier materials are returned through the beforementioned line 3 as a liquid medium for slurrying incoming coal.

In order to maintain the catalyst at an equilibrium level of activity and cleanliness, a slip stream is removed through line 20 and it passes into extraction zone 21. In extraction zone 21 the liquid catalyst is countercurrently contacted with solvent entering the lower portion of extraction zone 21 through line 22 and as a result of the countercurrent contact an extract stream consisting of solvent, antimony bromide, and hydrocarbon passes through line 23 into flashing zone 25 which is maintained at lower pressure. In flashing zone 25 solvent is separated from the extract stream and passes overhead through line 22 through which it is returned to the lower portion of extractor 21. The remainder of the extract stream is passed from the bottom of flashing zone 25 through line 26 and returned to the main body of catalyst. The material in line 26 consists almost entirely of the antimony tribromide and hydrocarbon that was removed in the slip stream passing through line 20.

The raflinate phase from extractor 21 consists of ash, char, and ammonia-antimony-bromide complex formed in the reaction zone 9. This material is introduced into regenerator 28 wherein it is subjected to high enough temperature to decompose the complex to form antimony bromide and ammonium bromide. If necessary, hydrogen bromide or bromine is also added to regenerator 28 so that regeneration may be better effected. The regenerated antimony bromide is returned to reactor 9 through line 30, either directly or by being added to the stream in line 20, while the residual material including ash and char is removed through line 31 and subjected to appropriate further treatment.

The process of the present invention may be varied in the manner of its performance without departing from the scope or spirit of the invention. For example, the process may be effected in two or more stages, with mixtures of catalytic metal halides, with various cleaning and regenerating schemes and in conjunction with other processes.

What is claimed is:

1. A process for producing normally liquid products from coal which comprises contacting coal with a continuous phase catalyst consisting essentially of metal halides selected from antimony trichloride, antimony tribromide, antimony triiodide, bismuth trichloride, bismuth tribromide and arsenic triiodide, said continuous phase maintained at a temperature of from about 200 to about 550 C. and under a hydrogen partial pressure of at least 250 p.s.i., and recovering normally liquid products therefrom.

2. The process of claim 1 wherein the continuous phase is maintained between 275 and 400 C.

3. The process of claim 1 wherein the hydrogen partial pressure is at least 800 p.s.i.

4. The process of claim 1 wherein unreactive solids are removed from said metal trihalide.

5. The process of claim 1 wherein said catalyst is subjected to regeneration reactions which convert ammoniametal halogen products to metal trihalide.

6. The process of claim 1 wherein the metal trihalide is antimony tribromide.

7. The process of claim 1 wherein the metal trihalide is antimony triiodide.

8. The process of claim 1 wherein the coal is introduced into the reaction zone as a slurry in liquid hydrocarbon.

References Cited UNITED STATES PATENTS 2,221,410 11/1940 Pier 208---8 2,087,608 7/1937 Pier et al. 208l0 1,938,542 12/1933 Pier et al. 20810 2,068,868 1/1937 Pier et a1 20810 2,606,142 8/1956 Storch 2081O 1,835,425 12/1931 Pier 20810 1,890,434 12/1932 Krauch et al. 20810 1,931,550 10/1933 Krauch et al. 20810 DELBERT E. GANTZ, Primary Examiner VERONICA OKEEFE, Assistant Examiner 

